1. Field of the Invention
The present invention relates to a resin composition for toners used in the development of electrostatic images in electrophotography and the like, and a toner that contains the resin composition.
2. Description of the Prior Art
Dry development methods are often employed for the development of electrostatic images in electrophotography, etc. Microgranular triboelectric developers containing dispersed colorlant such as carbon black, known as toners, are employed in these dry development methods.
Generally, the toner, charged by friction, adheres by electrical attraction to the electrostatic latent image on the photoconductor, thereby forming a toner image, which is then transferred onto a paper substrate. Next, this toner image is heated and compressed with a hot roller possessing appropriate surface release properties and heated to a specified temperature, thereby fusing the toner image onto the paper.
Such toners are required to possess physical characteristics as follows.
(1) Offset resistance (i.e., the toner does not cling to the hot roller or cleaning rollers, etc.)
(2) Good fixation (i.e., the toner adheres strongly and securely to the paper).
(3) Blocking resistance (i.e., the toner particles do not agglomerate).
In addition, since the hot roller may be operated at either low or high rotational speeds, the toner is exposed to varying temperatures, depending upon the speed of the hot roller, therefore, the toner must also possess the following property.
(4) Excellent offset resistance over a wide range of temperatures.
Resin compositions for toners prepared with a view to improvement of the above-mentioned characteristics have been described, i.e., resins crosslinked with metal ions obtained by a reaction between a polymer containing carboxyl groups and a multivalent metal compound (Japanese Laid-Open Patent Publication Nos. 57-178250 and 61-110155).
In addition, for example, Japanese Laid-Open Patent Publication No. 63-214760 discloses the use of a resin composition as a toner constituent, the composition containing (i) a resin cross-linked with metal ions obtained by a reaction between a comparatively low molecular weight polymer containing carboxyl groups and a multivalent metal compound, and (ii) a comparatively high molecular weight polymer.
The aforementioned types of previously existing resin composition for toners are comparatively satisfactory as regards the aforementioned characteristics (1) to (3), but are inadequate as regards characteristic (4), i.e., offset resistance over a wide range of fixing temperatures.
If the proportion of the aforementioned multivalent metal compound is increased or a high molecular weight polymer is used in order to improve the offset properties of the toner, then the adhesion of the toner to the paper substrate deteriorates.
The provision of a cleaning roller in contact with the hot fixing roller to remove the toner which has clung to the hot roller has also been proposed. However, in this case, the toner tends to accumulate on the cleaning roller.